You will have noticed that these are all auxiliaries. Some of them are also used as main verbs. As auxiliaries they help main verbs to form their tenses and moods. As anomalous finites they serve other purposes.

Note that anomalous finites are irregular verbs because they do not form the past tense in the regular manner by the addition of –ed, -d or –t, but by a change in the root vowel. Some anomalous finites such as must, ought, need and dare have no past tense forms at all.

These irregular verbs, however, are different from other irregular verbs in their function and hence are called anomalous finites or special finites.

One of the major differences is that unlike other finites, anomalous finites can be used along with n’t, the shortened form of not.

It isn’t true. (= It is not true.)
We aren’t coming. (= We are not coming)
You shouldn’t wait. (= You should not wait.)

Here is a list of the contracted forms of the anomalous finites + not. The uncontracted form is given in the brackets.